1. Field of the Invention
The invention relates to a method for providing a semiconductor wafer composed of silicon with an epitaxially deposited layer in an epitaxy reactor, comprising the following steps:
placing a dummy wafer on a susceptor of an epitaxy reactor;
conducting an etching gas through the epitaxy reactor in order to remove residues on surfaces in the epitaxy reactor through the action of the etching gas;
conducting a first deposition gas through the epitaxy reactor in order to deposit silicon on surfaces in the epitaxy reactor;
replacing the dummy wafer with a substrate wafer composed of silicon on a susceptor of the epitaxy reactor; and conducting a second deposition gas for depositing an epitaxial layer on the substrate wafer.
2. Background Art
A method for epitaxial deposition onto a substrate wafer is described in EP 1 533 836 A1, for example, which disclosed that it is advantageous and often necessary to remove residues from surfaces in the epitaxy reactor which have been deposited on these surfaces in an uncontrolled manner during the deposition of silicon on a substrate wafer. Such a step, referred to hereinafter as a “chamber etch,” is carried out more or less frequently depending on the degree of contamination and quality requirements. If the epitaxially deposited layer on the substrate wafer is 20 μm or thicker, or if there are particularly high quality requirements, it is expedient to carry out a chamber etch after the deposition of an epitaxial layer on one substrate wafer before a further substrate wafer is coated. In other cases, the chamber etch can also take place less frequently, for example after every 2nd to 8th coating of substrate wafers. EP 1 533 836 A1 also proposes coating the etched surfaces in the epitaxy reactor with a thin film of silicon by conducting a deposition gas through the epitaxy reactor. The thin film of silicon seals the surfaces and prevents contaminants that diffuse from the surfaces from passing into the growing epitaxial layer during a subsequent coating of a substrate wafer. The deposition of a thin film of silicon on surfaces of the epitaxy reactor after the chamber etch is referred to hereinafter as “chamber coating”.
DE 10 2005 045 337 A1 indicates that a chamber etch has a disadvantageous effect on the flatness of a substrate wafer subsequently coated with an epitaxial layer. Thus, in particular, the local flatness of such a semiconductor wafer is impaired. Therefore, it is recommended that the susceptor be hydrophilized after the chamber etch by means of a hydrophilic wafer being placed onto the susceptor for a short time. This procedure has the disadvantage that a dedicated method step is required for hydrophilizing the susceptor.
The chamber etch also has a disadvantageous effect on the lifetime of the minority charge carriers of a substrate wafer subsequently coated with an epitaxial layer. The lifetime of the minority charge carriers of such a semiconductor wafer, determined by microwave photoconductivity decay (“μ-PCD”), is significantly shorter than if chamber etch and chamber coating are dispensed with prior to the coating of a substrate wafer.
The chamber etch additionally has a corrosive effect on the susceptor and in particular on lift pins which are embedded in the bottom of the susceptor and which serve for raising and lowering the wafers. Susceptor and lift pins therefore have to be replaced comparatively often owing to wear as a result of corrosion.